The Parrish patent U.S. Pat. No. 2,988,782 discloses the manufacture of very fine polymer filaments that can be employed to manufacture water-laid sheets of synthetic paper. These synthetic filaments are of such a small diameter that they behave quite differently from spun filaments and have been characterized in the art as "fibrils" or "fibrids."
The Parrish process for preparing such fibrils involves preparing a solution of a polymer in a suitable solvent and adding the polymer solution to a vigorously-agitated solution of a liquid, which is a nonsolvent for the polymer of interest. As the polymer solution is added to the vigorously-stirred nonsolvent liquid, the droplets of the polymer solution are subjected to shear forces and attenuated while simultaneously being precipitated. Parrish discloses that the precipitation step is carried out in a high intensity mixer such as a Waring blender. While the Parrish process is suitable for making small laboratory quantities of such fibrils, the process is not well suited to make substantial quantities of the fibrils at an acceptable cost.
The Davis, et al, patent U.S. Pat. No. 4,013,751 discloses an alternate process for preparing fibrils by modified methods in which a hot polymer solution is passed through a Hammermill and subsequently cooled as the streams of polymer solution are thrown free of the rotating plate of the Hammermill. While this process provides good quality fibrils, the process is capital intensive and has higher manufacturing costs than is desired.
There is a need in the art for improved apparatus and processes for manufacturing fibrils at a lower cost.